In electronics systems, many devices and techniques have been developed to provide EMI/EMC shielding (EMI shielding prevents electromagnetic radiation from escaping. EMC shielding prevents electromagnetic radiation from entering.) Electronic components, such as printed circuit board (PCBs) for example, generate electromagnetic wave energy. Typically, each printed circuit board is separately housed within an enclosure. EMI/EMC shielding is desirable for two main reasons. It is desirable that electromagnetic wave energy generated by electronic components be contained to avoid adversely affecting or interfering with the operation of other electronic components. As well, it is desirable that electromagnetic wave energy generated from other electronic components be shielded from the electronic components to avoid interfering with the operation of the electronic components.
Typically, enclosures for electronics, such as PCBs, for example, have a top surface and a bottom surface and a separate gasket between the top surface and the bottom surface to provide EMI/EMC shielding. In some cases, each side of the electronics requires a gasket. Well-known types of gaskets include rope-like gaskets and spring finger gaskets.
Gaskets are often elastomeric and rope-like or string-like and contain or are coated with conductive particulate (gaskets must be electrically conductive in order to contain electromagnetic wave energy). In an enclosure having a top surface and a bottom surface, either the top surface or the bottom surface of the enclosure may have a guiding feature for routing the EMI/EMC gasket around the perimeter of the surface (or at least around the area where the PCB or electronic components will be located). The guiding feature also holds the gasket in place.
For the purpose of this example (ie: for ease of reference), the guiding feature is located within the top surface. The guiding feature is typically a "groove" formed within the top surface, with a width slightly less than the diameter of the rope gasket. To use the gasket, the one end of the gasket is usually manually pushed into one portion of the guide, and then the remaining length of the gasket is pushed into the guide around the perimeter of the surface.
When the top surface of the enclosure is then mated with the bottom surface, the EMI/EMC gasket will contact the bottom surface, thereby providing EMI/EMC shielding around the electronic components.
Because EMI/EMC gaskets often require that a guide be incorporated within either the top or bottom surface of the enclosure, and because such gaskets are often manually fitted around the perimeter of one surface, the use and installation of these types of gaskets tends to be relatively time-consuming and expensive. As well, the cost of manufacturing the top or bottom surface having a guide in addition to the cost of separately manufacturing such gaskets adds to the cost of the electronics system. In fact, the cost of manufacturing gaskets themselves is relatively high and is often the greatest single cost of the electronics packaging.
Instead of using rope-like gaskets, some electronics enclosures use spring finger gaskets (usually metallic). spring finger gaskets typically have a flat strip portion. The strip portion has a number of uniformly-spaced, biased fingers projecting from one surface. To use spring finger gaskets, a number of spring finger gaskets are adhered, typically either glued or clipped, to the top (or bottom) surface of the enclosure, around the area which will be occupied by the electronics. When the top surface is mated with the bottom surface, the spring fingers of the gasket will contact the bottom surface, thereby providing EMI/EMC shielding around the electronics.
Because spring finger gaskets must be manufactured separately from the top and bottom surfaces of the enclosure and because such gaskets must be manually or at least separately adhered to one surface of the enclosure, the installation of such gaskets tends to be time-consuming and the manufacture and installation of such gaskets tends to be relatively expensive.
In some cases, EMI/EMC gaskets cannot be re-used after disassembly. In some cases, EMI/EMC gaskets produce or require high clamping pressure, which necessitates stiff covers and a large number of fasteners. In some cases, EMI/EMC gaskets create galvanic corrosion problems due to dissimilar materials with respect to the electronics or enclosure components which results in degrading performance over time.
Accordingly, it would be desirable to have a gasket which is not separate from the enclosure and which does not require installation. In this regard, EMI "shield cans" are known, which are sheet metal enclosures for a PCB carrying electronic components. Some of the components are grouped together and it is one or more groups which are shielded by an EMI shield can. Typically, EMI shield cans consist of two main parts. A first part has four upstanding walls around the electronics. A second part fits over the four walls. The second part has a flat roof, to cover the area defined by the four wall. The second part also has evenly spaced, flexible fingers. When the second part is placed over the first part, the fingers securely hold the second part to the first part.
While EMI shield cans, by their design, are housings, electronic components typically have housings in addition to, or in any case, distinct from, EMI shield cans. These non-EMI shield can housings may have features lacking in EMI shield cans such as heat sinks, for example. It would be desirable to eliminate the need to have both EMI shield cans and another housing for a single substrate or the same electronic components. Further, because EMI shield cans are made from sheet metal, they suffer from the inherent limitations of sheet metal. For example, because EMI shield cans are made from sheet metal, the entire surface of the EMI shield can has the same thickness. In other words, by using sheet metal, it is difficult to vary the thickness of different portions of the EMI shield can. Further, when using sheet metal, it is difficult to include bosses and certain other features in the shield can. Moreover, non-EMI shield can housings are also typically needed, in part, to provide an aesthetically pleasing appearance for the user. Accordingly, it would be desirable to create EMI/EMC shields, capable of having varying thickness at different portions of the shield, capable of having bosses formed therein while also being integral with a housing for electronic components. It would also be desirable to incorporate other features common in moulded plastic parts, such as cosmetic features, snap fits, catches and other user interface features, such as handles, for instance.